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/**
*
* Copyright 2005 The Apache Software Foundation or its licensors, as applicable.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.tuscany.common.discovery.util;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.URL;
import java.security.AccessController;
import java.security.PrivilegedAction;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Enumeration;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.WeakHashMap;
import org.apache.tuscany.common.io.util.FixedURLInputStream;
//FIXME Port to 1.5 collections
/**
* A Registry for service providers defined using the
* <a href="http://java.sun.com/j2se/1.5.0/docs/guide/jar/jar.html#Service%20Provider">JAR service provider mechanism</a>.
*
*/
public class ServiceProviderRegistry {
private Map registry = Collections.synchronizedMap(new WeakHashMap());
private final static ServiceProviderRegistry instance = new ServiceProviderRegistry();
/**
* Constructor.
*/
public ServiceProviderRegistry() {
super();
}
/**
* @return Returns the instance.
*/
public static ServiceProviderRegistry getInstance() {
return instance;
}
/**
* Get the available providers of a given type.
*
* @param clazz
* @return
*/
public List getServiceProviders(final Class clazz) {
List providers = (List) registry.get(clazz);
if (providers != null)
return providers;
providers = (List) AccessController.doPrivileged(new PrivilegedAction() {
public Object run() {
return loadServiceProviders(clazz);
}
});
registry.put(clazz, providers);
return providers;
}
/**
* Get an provider of a given type.
*
* @param clazz
* @return
*/
public Object getServiceProvider(Class clazz) {
List providers = getServiceProviders(clazz);
if (providers.isEmpty())
return null;
else {
return providers.get(0);
}
}
/**
* Registers an provider programatically
*
* @param clazz
* @param provider
*/
public void registerServiceProvider(Class clazz, Object provider) {
getServiceProviders(clazz).add(provider);
}
/**
* Load providers of the given type
*
* @param clazz
* @return
*/
private List loadServiceProviders(Class clazz) {
List classNames = new ArrayList();
// First look for a system property named <SPI className>
String className = System.getProperty(clazz.getName());
if (className != null)
classNames.add(className);
// Find all the class names mentioned in all the META-INF/services/<SPI className>
ClassLoader loader = Thread.currentThread().getContextClassLoader();
try {
Enumeration files = loader.getResources("META-INF/services/" + clazz.getName());
while (files.hasMoreElements()) {
URL url = (URL) files.nextElement();
readClassNames(url, classNames);
}
} catch (IOException e) {
}
// Instantiate an provider for each of the named classes
List providers = new ArrayList();
Iterator i = classNames.iterator();
while (i.hasNext()) {
String name = (String) i.next();
try {
Class providerClass = Class.forName(name, true, loader);
providers.add(providerClass.newInstance());
} catch (Exception e) {
// Ignore ClassNotFoundException
}
}
return providers;
}
/**
* Read class names from the given URL.
* @param url
* @param classNames
* @throws IOException
*/
private void readClassNames(URL url, List classNames) throws IOException {
InputStream is = new FixedURLInputStream(url);
try {
BufferedReader in = new BufferedReader(new InputStreamReader(is, "UTF-8"));
String inputLine = null;
while ((inputLine = in.readLine()) != null) {
int i = inputLine.indexOf('#');
if (i >= 0) {
inputLine = inputLine.substring(0, i);
}
inputLine = inputLine.trim();
if (inputLine.length() > 0) {
if (!classNames.contains(inputLine)) {
classNames.add(inputLine);
}
}
}
} finally {
is.close();
}
}
}
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